CCN Spectra in ACE-1

Measurements of cloud condensation nuclei (CCN) concentrations
and spectral shape are summarized for ACE-1. These were obtained
with two nearly identical CCN spectrometers; one on the NCAR C-
130 aircraft and one at the Cape Grim monitoring station. Good
agreement between these two instruments was achieved during a
flyby of Cape Grim.

Vertical and temporal variations of CCN concentrations and
spectra are displayed. These often showed very low
concentrations in the vicinity of some clouds, which demonstrated
cloud scavenging, which was sometimes the site of high CN (total
particles most smaller than CCN) concentrations suggesting
particle production. As with previous maritime measurements
higher concentrations were often found above the boundary layer
(Hudson and Frisbie 1991) suggesting that this is the source of
particles for the boundary layer. Comparisons with CCN spectra
obtained with the same instruments in the earlier Southern Ocean
Cloud Experiment (SOCEX), which occurred in the same area at both
a similar time of year and during the opposite season, revealed
seasonal CCN variations. These may be due to differences in
natural ocean emissions of DMS, variations in cloud scavenging,
or variations in long range transport above the boundary layer.
CCN spectra are also expressed in terms of the number of soluble
ions to facilitate comparisons with aerosol chemistry
measurements.

Measurements of CCN volatility and size vs. supersaturation
(Hudson and Da 1996) from both ACE-1 and SOCEX are presented.
These demonstrate that most of the time most of the CCN act like
ammonium sulfate. Both of these sample processing mechanisms
seem to manifest distinct differences depending on whether the
particles had an anthropogenic origin. Differences in the
volatility of CN for northern and southern Hemisphere
measurements are noted.